How insoluble titanium anodes used in nickel plating baths?

How insoluble titanium anodes used in nickel plating baths?

During nickel plating, the anode provides electrical contact with the solution and distributes the current to the work being plated. In most cases, the plate uses nickel metal anodes which dissolve as the current flows and thereby replace the nickel ions discharged at the cathode, maintaining the concentration of nickel salts dissolved in the plating solution.

Small insoluble anodes made by titanium with a thin coating of platinum have been used to increase the current directed into recesses on a shaped part but such anodes give rise to other problems, such as exfoliation of the platinum deposit in presence of chloride ions, the replacement of depleted metal ions and the cost of the platinized electrode, etc. These problems can be overcome by using soluble nickel auxiliary anodes on electrical circuits separated from the main anodes.

Another way of directing current into the recess is to use a short nickel rod that has no external electrical connection but points into the recess. Since nickel is a metallic conductor, it acts as a low resistance path for the current.

Current from the main anode travels to the nearer end of the rod, through the rod, and then across the short distance, through the solution to the surface of the recess in the work. In consequence, nickel metal is deposited on the end of the rod near the anode and dissolved from the end near the cathode. An incidental advantage of such bipolar anodes is that if they are accidentally pushed against the work, there is no short-circuiting since the bipolar anode is not electrically connected to any of the electrodes.